The nucleotide sequence of the lacY gene predicts that the primary translation product is a single protein of MW equals 46,500. We have previously shown that two poly-peptides appear in the membrane in equimolar amounts following Y induction. Their MW's of 30,000 and 15,000 suggest that they may arise from proteolytic cleavage of the precursor form. To test this hypothesis, we will analyze the peptide patterns of both proteins after cleavage with CNBr for comparison with those predicted from the gene sequence. The composition and C and N terminal sequences of both polypeptides will be examined. Monoclonal antibodies to both the 30 and 15 kilodalton proteins will be prepared and used to examine their relationship to one another and as a probe for the precursor protein. Membrane active reagents will be used to attempt to block the processing event and allow precursor detection.